ORIGINAL ARTICLES The medial collateral ligament of the elbow joint: Anatomy and kinematics Sarah Floris, MS, Bo S. Olsen, MD, Michel Dalstra, PhD, Jens 0. Slzrjbierg, MD, and Otto Sneppen, MD, DMSc, Aarhus, Denmark Eighteen osteoligamentous elbow joint specimens were included in a study of the medial collateral ligament complex (MClj. The morphologic characteristics of the MCI were examined, and three-dimensional kinematic measurements were taken aher selective ligament dissec- tions were performed. On morphologic evaluation the MCI is divided into the anterior bundle and the posteri- or bundle. The anterior bundle can be divided into ante- rior and posterior bands. The maximum valgus and internal rotatory instab;/rIy after transection of the anteri- or band, I 7.7” and 7 I .2’, respectively, were found at elbow flexions of 30” and 40”. Severance of the entire anterior bundle produced major valgus and internal rotatory laxity through the complete flexion arc of maxi- ma/ 74.2” and 78.54 respective/y, at 70” and 60” of elbow flexion. Cutting both the posterior band and the posterior bundle resulted in only internal rotatory laxity of maximal 7.2” at 7 30” of elbow flexion. This study defines the anterior band as the primary constraint to valgus and internal rotatory forces, the posterior band as the secondary, and the posterior bundle as the ter- tiary constraint. The MC1 was observed to be a complex of ligamentous fibers rather than individual bands that stabilizes the joint against vagus and internal rotatory forces. (J Shoulder Elbow Surg I 998;7:345-5 1) The medial collateral ligament (MCL) of the elbow, also referred to as the ulnar collateral lig- ament, consists of three maior components: the anterior bundle, the posterior bundle, and a trans- verse part*t9(‘5 (Figure 1). The anterior bundle is From the Biomechanics Laboratory, Shoulder and Elbow Clin- ic, University Hospital of Aarhus. Reprint requests: Bo Sanderhoff Olsen, MD, Orthopaedic Research Fellow, Biomechanics Laboratory, Shoulder and Elbow Clinic, University Hospital of Aarhus, Building 1 A, Nerrebrogade 8000, Aarhus, Denmark. Copyright 0 1998 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/98/$5.00 + 0 32/l/84211 the most prominent component and can easily be distinguished from the joint capsule.15 This bundle gives restraint to valgus and internal rotatory loads.6~‘4~15~*4~*6,27 The posterior bundle is a fan- shaped thickening of the capsule. Sectioning of this bundle has been reported not to give any sig- nificant laxity to the elbow joint.6,16J4J7 The transverse part was noted not to contribute to the stability of the ulnohumeral joint, because it origi- nates and inserts on the ulna; therefore it will not be discussed further.15!*7 The origin of the medial ligamentous structures is not located in the axis of flexion. Therefore some fibers are taut in extension23J4 and some in flexion.15J4 Because of this, two functional com- ponents of the anterior bundle were defined : the anterior and the posterior band.*4,*7 Several stud- ies observed a sequential tightening of these bands proceeding from anterior to posteri- or4!1*J* when the elbow was flexed from full extension. Fuss4 defined isometric fibers between the anterior and the posterior band and called these the guiding bundle. Only recently, the func- tion of the two bands of the anterior bundle has been studied after separate sectioning.* It was concluded that the anterior band is the primary constraint to valgus loads, and the posterior band is a coprimary constraint only at 120” of elbow flexion. However, until now the function of the dif- ferent bands has not been analyzed through the entire flexion range. On clinical evaluation medial elbow instability is not common and usually has a traumatic origin. A fall on the outstretched hand applies both a val- gus stress and an external rotatory moment on the elbow joint.l8!‘9 This can result in a partial or a complete rupture of the anterior bun- dle.7~8~11J’7,‘9J4 Another cause for medial elbow instability is throwing injuries such as in baseball pitching as a result of repeated extension stress- 345